Project Summary/Abstract Alcohol (ethanol; EtOH) abuse is a leading cause of death and disability, making our understanding of the mechanisms that affect transition from healthy use of EtOH to development of an alcohol use disorder (AUD) a high biomedical priority. In this context, the initial neurological responses to socially relevant concentrations of EtOH (5-20mM), and individual differences in those responses are thought to play a critical role in determining vulnerability or resilience to development of AUD. Thus, it is crucial to identify molecular targets and neural circuit responses to low concentrations of EtOH, and to identify the mechanisms by which such responses vary across individuals with high or low risk for developing AUD. In our published and preliminary studies, we have determined that low concentrations of EtOH (10mM, as would occur in the blood of an average adult human after consuming 1-2 standard alcoholic beverages) powerfully affect cerebellar granule cell GABAAR currents, but with opposite polarity in multiple strains of rodents with high and low EtOH consuming phenotypes respectively. Further, we have discovered a previously unknown direct synaptic connection between the cerebellum and the ventral tegmental area (VTA), a brain structure known to influence many aspects of EtOH reward and associated behaviors. These are important discoveries because genetic differences in cerebellar structure, connectivity and sensitivity to EtOH are known to be associated with risk for developing an AUD in humans and with excessive EtOH consumption in rodents, but the underlying mechanisms are unknown. The purpose of this proposal is to advance our understanding of how low concentrations of EtOH affect cerebellar spatiotemporal processing and behaviors, how such actions vary in strains of mice with divergent EtOH related behavioral phenotypes, and to characterize the neural circuitry that translates differential actions at a cellular level into differential behavior, including EtOH reward and excessive EtOH consumption. Success in this endeavor will increase our understanding of how the cerebellum influences predilection to developing an AUD, and will identify novel molecular targets for manipulating responses to low concentrations of EtOH. Collectively, such information should help guide the development of psychological and pharmacological approaches to screening for and deterring development and maintenance of AUD. We will use a combination of patch-clamp recording from cerebellar brain slices, patterned optical light stimulation (to simulate in vivo-like network processing), and behavioral techniques combined with optogenetic manipulations of cerebellar processing to determine how low concentrations of EtOH affect cerebellar processing and output, and EtOH related behaviors. We will then use optogenetic tract tracing techniques to fully characterize cerebellar to VTA circuitry and function, which will provide important insight into the neural circuitry that translates differential actions of EtOH in the cerebellum to divergent EtOH-related behavioral phenotypes. Successful completion of the proposed experiments will improve our understanding of the cellular mechanisms and neural circuitry that influences predilection to AUD.